Microbiological-scaled sterility controls

ABSTRACT

A METHOD AND APPARATUS FOR DETERMINING THE EFFECTIVENESS OF A STERILIZING CYCLE BY PREPARING A PLURALITY FOR EXAMPLE SEVEN SPORE IMPREGNATED STRIPS OF FILTER PAPER SEALED IN GLASSINE ENVELOPES AND EXPOSING THE STRIPS TO THE STERILIZING CYCLE UNDER STUDY. EACH OF THE SEVEN STRIPS HAS A DIFFERENT SPORE POPULATION, E.G. 10**3, 10**4, 10*:5, 10**6, 10**7, 10**8, AND 10**9. THE STERILITY CONTROL IS EITHER EXPOSED DIRECTLY TO THE ACTIVE ELEMENTS OF THE STERILIZING PROCESS OR THE CONTROL IS PLACED IN THE LOAD OF MATERIALS TO BE STERILIZED. THE STRIPS ARE THEN REMOVED AND INCUBATED AND STUDIED. THE EFFECTIVENESS OF THE CYCLE CAN BE CONCLUDED FROM THE SPORE STRIP CONTAINING THE HIGHEST POPULATION ON WHICH THE ENTIRE POPULATION IS KILLED.

Jan. 16, 1973 K KERELUK MICROBIOLOGICAL-SCALED STERILITY CONTROLS FiledSept. 15, 1969 Nm m .SLN

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BY KARL /ERfL-UK aux /M AUM/var.

United States Patent O M MICROBIOLOGICAL-SCALED STERILITY CONTROLS KarlKereluk, Fairview, Pa., assignor to American Sterilizer Company, Erie,Pa. Filed Sept. 15, 1969, Ser. No. 857,668 Int. Cl. C12k 1/04 U.S. Cl.195--103.5 R 14 Claims ABSTRACT F THE DISCLOSURE A method and apparatusfor determining the effectiveness of a sterilizing cycle by preparing aplurality for example seven spore impregnated strips of filter papersealed in glassine envelopes and exposing the strips to the sterilizingCycle under study. Each of the seven strips has a different sporepopulation, e.g. 103, 104, 105, 106, 107, 1018, and 109. The sterilitycontrol is either exposed directly to the active elements of thesterilizing process or the control is placed in the load of materials tobe sterilized. The strips are then removed and incubated and studied.The effectiveness of the cycle can be `concluded from the spore stripcontaining `the highest population on which the entire population iskilled.

STATEMENT OF THE INVENTION This invention relates to sterility controls,and more particularly, to control devices for determining theeffectiveness of a sterilizing cycle.

OBJECTS OF THE INVENTION It is an object of the invention to provide animproved sterility control.

Another object of the invention is to provide an improved control fordetermining the effectiveness of a sterilizing cycle.

Another object of the invention is to provide an improved structure of asterility control.

Another object of the invention is to provide a sterility control, whichis simple in construction, economical to manufacture, and simple andefliicient to use.

Another object of the invention is to provide an improved method ofcontrolling a sterilizing process in a sterilizer.

GENERAL STATEMENT OF THE INVENTION It is well known in the field ofsterilization that the sterility of an article or commodity ispredicated in its exposure to fairly precise conditions which cannot bevaried to any great extent without sacrificing sterility. In many cases,even slight variations in exposure conditions may result in so-calledhits or misses or situations where sterility may be achieved on oneoccasion, fail on the next and succeed on the third attempt even thoughthe test conditions were supposedly the same each time.

Because of these situations, a method is hereby proposed which enablesan operator or manufacturer of sterile disposables to evaluate theeffectiveness and/or eiciency of the sterilizing process. With thismethod, it is possible to determine (1) whether the conditions of theprocess are capable of achieving sterility, (2) whether the Iconditionsof the process will achieve sterility each time the process isconducted, and (3) whether some safety factor, such as increasedexposure time or increased temperature, should be considered in order toattain sterility and/or reproducibility of results.

DESCRIPTION OF THE PROCESS The proposed method is based on the use ofspecially prepared bacterial spore-impregnated strips of filter paper,

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sealed in glassine envelopes and exposed'to the conditions of thesterilization process under study, and the proper interpretation of thetest results.

The bacterial spore-impregnated strips, employed in this method, areprepared in a manner similar to currently used spore strips with oneexception. A total of seven spore strips are prepared as a set with eachstrip containing a different concentration or population of bacterialspores, i.e., the first strip will contain a population of 1 10zbacterial spores, the second strip will contain a population of 1 103spores, and so on until the final or seventh strip will contain apopulation of 1 108 bacterial spores.

The organism used in this method comprises albacterial sporeformingspecie known to be resistant to the sterilizing process being used ortested. For example, the bacterial specie used to test the eiiiciency ofa steam sterilizing proc'- ess is usually Bacillus stearothermophilus,while Bacillus subtilis var. niger is more commonly employed to test theefiiciency of such sterilizing processes as dry heat or ethylene oxide.

In practice, the microbiological-scaled sterility controls are exposedeither directlyto the sterilization process or are placed in the load ofmaterials to be sterilized. The sterilization process is conducted inthe usual manner following which the sterility controls are removed fromthe sterilizing apparatus or the load, aseptically removed from theirrespective glassine envelopes and cultured in tubes of recommendedbacteriological culture media. The tubes are then incubated at theoptimum temperature of the test organism (usually stipulated on theglassine envelope) for a period of seven days. Results are recorded interms of growth or no growth.

On the basis of the results, the effectiveness and/or efficiency of thesterilizing process under the conditions employed can be determined. Toillustrate, in the event that the sterility `control strips coveringspore populations ranging from 102 to 106 are sterilized but thosestrips containing 10'7 through 108 spores are not sterilized, it can beconcluded that the sterilizing conditions used are capable ofsterilizing materials containing microbial contamination levels upthrough 1 10 organisms. If successive tests produce the same result, itcan be concluded that the conditions of the sterilizing process arereproducible and will provide consecutive sterilizing cycles. However,if the above results are not achieved in each successive cycle, it

can be concluded that the sterilizing conditions are not capable ofproducing reproducible results and will require some modification. Ifall seven of the lsterility control strips are repeatedly sterilized, itcan be concluded that the sterilizing conditions are capablev ofsterilizing materials or articles which are unusually heavilycontaminated. How- EXAMPLE (1) Sterile carriers (Spordex strips andceramic tiles) were inoculated with Varied spore populations (103, 104,105, 106, 10", 10B, 109).

(2) They were exposed to 500 mg./l. of Eto 50% R.H. and F. at variedtime intervals. The shortest period of exposure for the inoculatedcarriers was five minutes. The exposure period was increased -to 30minutes by five-minute increments.

(3) At each exposure period for each of the seven populations 10inoculated carriers were exposed (5 spordex strips, 5 ceramic tiles) tothe test conditions. After exposure each carrier was transferredindividually to a tube of Trypticase Soy Broth(TSB). The tubes wereincubated at 37 C. for one week. Following incubation each tube of TSBwith a carrier `was observed for the presence or absence of growth.

STATEMENT OF PRIOR ART Test strips have been used for various purposesto indicate various intensities of process, for example, Pat. 3,245,-S82.l discloses a test strip for testing the phenylalanine in blood.

FIG. 1 isfan isometric view of one embodiment of the invention.

FIG. 2 is a top view of another embodiment of the invention.

v FIG. 3 is a cross-sectional view taken on line 3 3 of FIG-2. f

FIG. 4 is a cross-sectional view taken on line 4--4 of FIG. 2.

FIG. 5 is aview showing the embodiment of FIG. v2 folded.

FIG. 6 is a view showing the embodiment of FIG. '2 formed into a roll.

Now with more particular reference to the embodimen of FIG. 2 through 6,the glassine envelopes are indicated at 10. They are divided intocontainers 11, 12, 13, l14, 15, 16, 17, and 18 by they scored lines 19,20,21, 22, 23, and 24. The material which makes up the envelope may bemade of a sheet which is folded back on itself at and sealed along lines26 and 27 by a suitable process. A spore carrier 28 will be enclosed ineach compartment of the envelope. The spore carrier 28 will be speciallyprepared bacterial spore impregnated strips of lter paper, sealed in theglassine envelopes, and they will be exposed to the condition ofsterilizing by placing the envelope 10 either rolled up, as shown inFIG. 6, or folded, as shown in FIG. 5, or lying at as shown in FIG. 2.

Inthe embodiment of the invention shown in FIG. l a container 110 isshown, which is made of relatively rigid material and which hascompartments 111, 112, 113, 114, 115, 116, 117. The compartments willeach contain at least one bacterial sporey impregnated strip 118, 119,120, 121, 122, 123, and 124. The strips will be made according to a wellknown process, such as for example shown in Pat. No. 2,931,757, and willbe impregnated with different numbers of spores, for example, sporestrips 118 through 124 will be impregnated with 1 1O2 bacterial spores,1 103 bacterial spores, 1 104 bacterial spores, on through 1X1()8bacterial spores, respectively.- A scored liner 126 .formed in the wallsof the compartments, by which the upper` part 127 ofthe container may beremoved. The spore strip may then be removed and incubated. Thecontainer 110 may be molded from a plastic material for example vinyl orpolyethylene.

The'embodiments. of the invention in which an exclusive property orprivilege is claimed are defined as follows: 1., A method of determiningthe etfectiveness of a sterilizing cycle comprising providing a set ofat least seven spore carrying devices, each having a different sporevpopulation, f

the numberv ofv spores in each said populationfbeing equal to a realpositive integer greater than zero raised to a real positive exponentialinteger, each said exponential power being different from the others,exposing said set4 of devices to the sterilizing cycle, f incubatingsaidA devices and observing the devices having the highest populationthat is completely killed. 2, The;l method`reeitedin claim 1 whereinsaid devices are inoculated'y with at least 102, 103, 104, 105, 106,10,and 1,08' spores'respectively,

saidspores are inoculated` with spores taken from the group of Bacillusstearothermophilus and Bacillus .subtilis var. niger. f

3. The process recited in claim 2 wherein said spore devices areincubated after exposure.

4. A sterility control comprising a plurality of containers adapted tobe disposed in a sterilizing chamber,

a spore carrier in each said container,

each said spore carrier being impregnated with a different population ofspores,

the number of spores in each said population being equal to arealpositive integer greater than zero raised to a real positive exponentialinteger, each said exponential power being different from the others,whereby the effectiveness of the cycle can be determined byobservingsaid spore carrier having the largest number of said sporeswherein all said spores are killed.

5; The control recited in claim 4 wherein said containers are connectedtogether in edge to edge relation.

6. The control recited in claim S wherein said containers are inthe formof glassine envelopes.

7. The control recited in claim 6 wherein said envelopes are adapted tobe disposed in said sterilzer in the form of a roll.

8. The control recited in claim l7 wherein at least seven l of saiddevices are provided in said containers.

y9. A container having at least seven separate compartments,

said compartments being isolated from each other,

a spore strip in each said compartment,

each said strip being impregnated with a different population of sporesfrom the other strips, the number of spores in each said populationbeing equal to a real positive integer greater than zero raised to areal positive exponential integer, each said exponential power beingdifferent froml the others,

said container with said spore strips being adapted to be placed in asterilizing chamber during sterilizing cycle and said stripssubsequently incubated and the strips having all spores thereon killedwhereby the effectiveness of said cycle can be determined by observingthe said strip having the largest number of said spores wherein all saidspores are killed.

10. The control recited in claim 9 wherein said compartments aregenerally rectangular incross section.

11. The control recited in claim 9-whe1'ein said containers are in theform of glassine envelopes, and a removable cover on each envelope,

said envelope being scored along a line adjacent on edge whereby thecovercan be removed.

12. The control recited in claim 9vwherein said con tainer is scoredadjacent one edge whereby said covermay be removed and said containerisV made in the form of glassineenvelopes attached together..

13. The control recited in claim 9 wherein said container is made of arelatively rigid material.. l

14. vThe control recited in claim 13 wherein said container is made.from a material taken from the groupv of vinyland polyethylene. 1`

References Cited UNITED STATES'PATENTS.

5/1960 Rdzok et al. 195-103.5

OTHER REFERENCES Brewer et al.: 1. Pharm. Sci. 50117142 (1961).

A. LOUIS MONACELL,` Primary Examiner M. D. HENSLEY, Assistant ExaminerU.S. Cl. XR.

